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First time accepted submitter kandelar writes "PBS recently ran a story about how some scientists are using human hair to trace where a person has been. The combinations of different isotopes in water make for somewhat unique signatures from place to place. These isotopes get placed in growing hair strands which can then be traced back to identify where a person has been."

where the protagonists are would-be thieves or revolutionaries who seem to have all the superstitiousness of medieval peasants, but it turns out that it's merely behaviour to defend against such high-tech genetic snooping.

I say that because this kind of technology has been around for many years. But hair or otherwise, location by isotope has so far turned out to be a boondoggle.

For example, for years TV shows (and the FBI themselves) claimed that they could trace ammunition to the manufacturer by the particular isotopic composition of the lead in bullet fragments.

False. It just isn't reliable. They did it for years, and it just doesn't work. The better the technology got, the more unreliable it was shown to be. Lead formulations change; suppliers change; the very ore from which the lead is refined, varies even from the same mine. Convictions were overturned.

In some ways, it parallels the evolution of DNA as evidence: it is far, far less reliable than it was first made out to be. Not only is it ridiculously easily contaminated, it can be deliberately planted, even more easily.

Hmm, we take a small snip of your hair, we find sea salt and silica dust, a spandex fiber, traces of sunblock and tanning lotion and a tiny crumb from a hotdog bun. Looking at all these elements and their isotopes we can say without a doubt, you spent Sunday at Venice Beach. Oh, and the smaller traces of Avian and Perrier tell us you think you're a snob and have no imagination. Haven't you ever heard of Badoit or Volvic? OH! and a flea! You have a dog.

Having lived in very dry places. (It frequently gets below 5% humidity in the summer outdoors) I know that with low humidity you can dry out fairly quickly. In Phoenix you are allowed to carry water into most sporting events because you need to replace the water that evaporates and everyone does it in the summer.

When you are in someplace that is humid, you do not dry out as quickly because the water is being replaced by water in the air (yet I know there are other factors),

It would be interesting to strictly control the isotope content in diet/drink for a month but in two different regions and then do a comparison.